Social media has become widely used and along this widespread use has arisen a request to know locations related to users (for example residences or work places). For example, if a user sends disaster information, the location of the user can be quickly estimated and necessary measures can be taken. Furthermore, if the locations of users can be estimated, sales promotions targeted at each individual region will be possible. On the other hand, social media typically includes fields for users to fill in their profiles and make the user profiles public. However, only a small minority of users fill in their exact locations in the profile fields. For example, it has been reported that a little more than 20% of the users of a social media filled in their exact locations in the profile fields. Various approaches to circumventing the problem have been attempted. For example, an approach has been attempted in which latitude/longitude information called a geotag is added to information to be sent by users by using a GPS (Global Positioning System) function of a mobile device (see Non-patent Literature 3). Another technique has been proposed that analyzes a text in sent information to estimate a location from a geographical name contained in the text (see Patent Literatures 1 and 2).
A technique has been proposed that estimates the location of a user from regionality of words (words specific to a particular region and dialect) used in a posted text to estimate the location of the user (see Non-patent Literature 1). Another technique has been proposed that takes into consideration the relationship between users (follow/followed relationship) that is implemented in social media to estimate the location of a user on the assumption that regionality is reflected in the relationship (Non-patent Literature 2).